Copolymers of polyaspartic acid and polycarboxylic acids and polyamines

ABSTRACT

Copolymers of polyaspartic acid which are suitable for the inhibition of scale deposition were obtained by reacting maleic acid, an additional polycarboxylic acid and ammonia in a stoichiometric excess, at 120°-350° C., preferably 180°-300° C., to provide copolymers of polysuccinimide. In a second embodiment, a polyamine was added to the reaction mix. These intermediate polysuccinimide copolymers could then be converted to the salts of copolymers of polyaspartic acid by hydrolysis with a hydroxide. 
     Such copolymers are useful in preventing deposition of scale from water and find applications in treating water. Other applications include scale prevention additives for detergents. In addition, such copolymers inhibit dental tartar and plaque formation.

This application is a divisional application of U.S. patent applicationSer. No. 07/994,922, filed Dec. 22, 1992, U.S. Pat. No. 5,408,028.

FIELD OF THE INVENTION

This invention relates to a process for the production of copolymers ofpolysuccinimide, their conversion to salts of copolymers of polyasparticacid and the use of these materials.

BACKGROUND OF THE INVENTION

Polyaspartic acid is a peptide chain in which amide linkages extend thechain in the thermal polymerization of aspartic acid, thestereochemistry of the aspartic acid is racemized and the formation ofboth α and β carboxylic acid groups have the ability to react to formsuch amide bonds. Such materials have been used for fertilizers andscale inhibition agents. They are particularly useful for the preventionof scale deposition in boiler water, reverse osmosis membranes,detergents and as inhibitors of dental tartar and plaque formation(tartar barrier agents). These materials are readily biodegradable.Methods for the preparation of polyaspartic acid have been developed(See U.S. Pat. Nos. 5,057,597 and 4,839,461 and U.S. patent applicationSer. No. 07/882,919, filed May 14, 1992, Louis L. Wood, and U.S. patentapplication Ser. No. 07/926,242, filed Aug. 7, 1992, Louis L Wood).

Biodegradability, calcium ion exchange ability and the disruption ofcalcium salt crystal structure are important properties of materialsused in the prevention of scale deposition in boiler water, on reverseosmosis membranes, in detergent use and as inhibitors of dental tartarand plaque formation (tartar barrier agents). We searched foreconomically useful materials, having a greater retention on the objectwherein inhibition of scale deposition is desired. Other desirableproperties were greater stability to biodegradation in addition tointrinsic value for the prevention of scale deposition in boiler water,on reverse osmosis membranes, during detergent use and as inhibitors ofdental tartar and plaque formation (tartar barrier agents). We havefound that the addition of polycarboxylic acids in the thermalpolymerization of maleic acid or aspartic acid produced novel and highlyeffective copolymers which possessed these properties.

DESCRIPTION OF RELATED ART

A number of methods of preparation of polyaspartic acid are disclosed inthe literature and other patents, however, no mention is made of methodsof preparation of copolymers of polysuccinimide and polycarboxylic acidswhich may then be converted to copolymers of polyaspartic acid andpolycarboxylic acids.

SUMMARY OF THE INVENTION

Copolymers of polysuccinimide were prepared by reacting maleic acid,ammonia and a polycarboxylic acid at temperatures greater than 120° C.These copolymers could be converted to copolymers of polyaspartic acidby addition of a hydroxide.

In a second embodiment of the invention, copolymers of polysuccinimidewere prepared by reacting maleic acid, ammonia, a polycarboxylic acidand a polyamine at temperatures greater than 120° C. These copolymerscould be converted to copolymers of polyaspartic acid by addition of ahydroxide.

One object of this invention is to provide a means of preparingcopolymers of polysuccinimide. A further object of this invention is toprovide a means of preparing copolymers of polyaspartic acid. Yetanother object of this invention is to provide novel compositions whichare useful for the inhibition of salt deposition, especially bivalentmetal salts, whether in water treatment, detergent addition, oral healthcare or cosmetic formulation. Yet another object of this invention is toprovide novel compositions which may be further reacted to provideuseful compounds for water treatment, cosmetics, oral health care anddetergents.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Copolymers of polyaspartic acid which are suitable for the inhibition ofscale deposition may be obtained by reacting maleic acid, an additionalpolycarboxylic acid and ammonia in a stoichiometric excess, at 120°-350°C., preferably 180°-300° C., and then converting the copolymer ofpolysuccinimide formed to a salt of a copolymer of polyaspartic acid byhydrolysis with a hydroxide.

In a second embodiment, copolymers of polyaspartic acid which aresuitable for the inhibition of scale deposition may be obtained byreacting maleic acid, an additional polycarboxylic acid, ammonia in astoichiometric excess, and a compound having 2 or more primary orsecondary amine groups per molecule, at 120°-350° C., preferably180°-300° C., and then converting the copolymer of polysuccinimideformed to a salt of a copolymer of polyaspartic acid by hydrolysis witha hydroxide.

The reaction is carried out first by the addition of water to maleicanhydride, thus forming maleic acid, or to maleic acid itself, and thepolycarboxylic acid, followed by addition of the appropriate amount ofammonia in the form of gaseous ammonia or as its aqueous solution. Atthis point, the polyamine may be added to either of these alternativeembodiments. This solution is then heated to remove water. As water isremoved, the mixture becomes a solid and then a melt of the mixture isformed. Water removal continues as the reaction proceeds and thetemperature is brought to 120°-300° C. When the theoretical quantity ofwater formed in the production of the copolymer of polysuccinimide hasbeen removed, which, depending on the temperature, may occur in evenless than 5 minutes, the reaction mixture is allowed to cool. Typically,it may take over 4 hours at 120° C., whereas it may take less than 5minutes at 300° C. The copolymer of polysuccinimide formed can be usedto make other novel and useful products by reactions such as thosedescribed in U.S. Pat. No. 4,363,797 or U.S. Pat. No. 3,486,380, whereinuseful derivatives for cosmetic use are described. The copolymers ofpolysuccinimide can also undergo alkaline hydrolysis to provide theappropriate salt of a copolymer of polyaspartic acid. Furthermanipulation to remove the water or the salts can be carried out toprovide water free powders of the salts or the free acid.

The polyamines which may be used to produce these copolymers of thisinvention have been described in U.S. patent application Ser. No.07/926,242, filed Aug. 7, 1992, Louis L. Wood, incorporated herein byreference, are amines which have at least two or more primary orsecondary amines available for reaction. Preferred polyamines have atleast two primary amine groups. The concentration may range from greaterthan 0 to 50%, however, the preferred range is greater than 0 to 30%.

Any aliphatic or aromatic polycarboxylic acid may be used in thisinvention, but the preferred acids are adipic acid, citric acid, fumaricacid, malic acid, malonic acid, succinic acid, glutaric acid, oxalicacid, pimelic acid, itaconic acid, nonanedioic acid, dodecanedioic acid,octanedioic acid, isophthalic, terphthalic and phthalic acid. Theconcentration may range from greater than 0 to 50%, however, thepreferred range is greater than 0 to 30%.

The hydroxides useful in converting the copolymers of polysuccinimideformed above to copolymers of polyaspartic acid Include, but are notlimited to, the alkali and alkaline earth metals and ammonia, examplesof which as their cations are, Na⁺, K⁺, Mg⁺, Li⁺, and Ca⁺⁺, Zn⁺⁺, Ba⁺⁺,Co⁺⁺, Fe⁺⁺, Fe⁺⁺⁺, and NH₄ ⁺.

Polysuccinimide is the imide form of polyaspartic acid and is also knownas anhydropolyaspartic acid.

The term "succinimide" is understood in the art to include many of theamide, imide and amidine species which are also formed by this reaction.The predominant product however is succinimide and this term is used torefer to the thermally polymerized reaction product of maleic acid andammonia or a polyamine. The polyaspartic moieties formed by hydrolysisof the polysuccinimides formed would be principally α and β aspartates.

The copolymers of polyaspartic acid provided by the present inventionare advantageous for inhibition of scale deposition in water treatment,as detergent additives, in oral health care or in cosmetic formulation.Solutions of the salts of copolymers of polyaspartic acid formed in thismanner have excellent scale inhibition performance. Salts which may beinhibited are the salts of Mg, Ca, Sr, Ba, and Ra. The carbonate,sulfate and phosphate salts are those in which greatest inhibition isshown.

The following examples are by way of illustration and not by way oflimitation.

EXAMPLE 1

Preparation of a polyaspartic acid/citric acid copolymer.

A slurry of 19.6 g (0.2 mole) maleic anhydride was dissolved in 40 mlwater at 80°-95° C. and 4.2 g (0.02 moles) of citric acid monohydrate(Formula weight 210) was added and the mixture was stirred until allsolids were in solution, after which the mixture was allowed to cool to25° C. To this solution at 25° C. was added 60 g of 30% aqueous solutionof ammonium hydroxide (0.44 mol NH₃). This solution was evaporated todryness over a period of 8 minutes. The solid was then heated at235°-245° C. for 5 minutes, removed from the heat, allowed to cool andbroken up with a spatula. The solid was then heated at 235°-245° C. fora second 10 minute period, removed from the heat, allowed to cool andbroken up with a spatula. Finally, the solid was heated at 235°-245° C.for a third 10 minute period, removed from the heat and allowed to coolto room temperature. The resulting water insoluble copolymer ofpolysuccinimide and citric acid (21.7 g) was slurried in 29.1 ml ofwater and a solution of 8.0 g of sodium hydroxide in 12 ml of water wasadded over 5 minutes. The solution was stirred for 10-20 minutes to givea clear red-brown solution of a copolymer of polyaspartic acid andcitric acid.

EXAMPLE 2

Preparation of a polyaspartic acid/succinic acid copolymer.

A slurry of 19.6 g (0.2 mole) maleic anhydride was dissolved in 40 mlwater at 80°-95° C. and 2 g (0.02 moles) of succinic anhydride (Formulaweight 100) was added and the mixture was stirred until all solids werein solution, after which the mixture was allowed to cool to 25° C. Tothis solution at 25° C. was added 60 g of 30% aqueous solution ofammonium hydroxide (0.44 mol NH₃). This solution was evaporated todryness over a period of 8 minutes. The solid was then heated at235°-245° C. for 5 minutes, removed from the heat, allowed to cool andbroken up with a spatula. The solid was then heated at 235°-245° C. fora second 10 minute period, removed from the heat, allowed to cool andbroken up with a spatula. Finally, the solid was heated at 235°-245° C.for a third 10 minute period, removed from the heat and allowed to coolto room temperature. The resulting water insoluble copolymer ofpolysuccinimide and succinic acid (21.9 g) was slurried in 29.1 ml ofwater and a solution of 8.0 g of sodium hydroxide in 12 ml of water wasadded over 5 minutes. The solution was stirred for 10-20 minutes to givea clear red-brown solution of a copolymer of polyaspartic acid andsuccinic acid.

EXAMPLE 3

Precipitation assay for calcium sulfate.

The material to be tested as an inhibitor of scale formation was addedin appropriate quantities to a solution of 5 ml of calcium chloridesolutions (21.6 g/L of CaCl₂ dihydrate and 41.4 g/L of NaCl) and 5 ml ofsulfate solution (20.9 g/L of Na₂ SO₄ and 41.4 g NaCl). The mixture wasthen placed in an oven at 160° F. for 3 hours. Finally the mixture wasfiltered through Whatman #2 paper and dried at 160° F. for 8 hours,after which the weight of precipitate was determined.

The polycarboxylic acid/polyaspartic acid copolymers were tested in theabove assay. The results are given below in Table 1.

                  TABLE 1                                                         ______________________________________                                                         polycarboxylic                                                                            weight of                                        compound         acid        precipitate (mg)                                 ______________________________________                                        blank                        44                                               polyacrylate, 5000 molecular 46                                               weight                                                                        copolymer polyaspartate/                                                                       citric acid 16                                               citrate                                                                       copolymer polyaspartate/                                                                       succinic acid                                                                             13                                               succinate                                                                     ______________________________________                                    

The copolymers of polyaspartic acid and polycarboxylic acids were veryeffective agents for the inhibition of mineral scale.

EXAMPLE 4

Calcium oxalate titration.

A 0.25 g sample of the sodium salt of the polyaspartic/citric acidcopolymer prepared in Example 1 was placed in a beaker with 100 ml ofdeionized water and 1 ml of 3% sodium oxalate was added. The solutionwas titrated with 0.1 mol of calcium chloride till the slurry turnedwhite.

Duplicate samples gave values of 6.4 and 6.6 ml. Sodium tripolyphosphategave required 8.2 and 8.1 ml while a polyaspartic acid prepared fromdiammonium maleate required 8.3 and 8.5 ml. This shows thatpolycarboxylic acid copolymers of polyaspartic acid are effectivecalcium chelators.

EXAMPLE 5

Preparation of a polyaspartic/citric acid copolymer with a polyamine

A solution of 2.1 g (0.01 moles) of citric acid monohydrate (Formulaweight 210) and 0.32 g (0.0028 moles) hexanediamine was added to 19.6 g(0.2 mole) maleic anhydride which had been dissolved in 40 ml water at80°-95° C., and finally 30 g of 30% aqueous solution of ammoniumhydroxide (0.22 mol NH₃) was added. This solution was evaporated todryness over a period of 30 minutes. The solid was then heated at195°-220° C. for 10 minutes, removed from the heat, allowed to cool andbroken up with a spatula. The solid was then heated at 230°-245° C. for10 minutes, removed from the heat, allowed to cool and broken up with aspatula. Finally, the solid was heated at 230°-245° C. for 10-15minutes, removed from the heat and allowed to cool to room temperature.The resulting water insoluble polymer was slurried in 40.0 ml of waterand a solution of 8.0 g of sodium hydroxide in 12 ml of water was addedover 5 minutes. The solution was stirred for 10-20 minutes to give aclear red-brown solution, pH 10-11.0 of a copolymer of polyasparticacid, citric acid and hexanediamine. The tests for CaSO₄, Example 3, andCaCO₃ (below) were run and the result are recorded in Table 2.

Inhibition of calcium carbonate precipitation by the calcium driftassay.

In this assay a supersaturated solution of calcium carbonate is formedby adding 29.1 ml of 0.55M NaCl and 0.01M KCl to 0.15 ml of 1.0M CaCl₂and 0.3 ml of 0.5M NaHCO₃. The reaction is initiated by adjusting the pHto 7.5-8.0 by titration with 1N NaOH and addition of the material to betested for inhibition of CaCO₃ precipitation at a level of 1.7 ppm. Atthree minutes, 10 mg of CaCO₃ is added and the pH is recorded. Thedecrease in pH is directly correlated to the amount of CaCO₃ thatprecipitates.

                  TABLE 2                                                         ______________________________________                                                      CaSO.sub.4 ppt                                                                          CaCO.sub.3 Drift                                      Sample        (mg)      (pH units)                                            ______________________________________                                        none          84        .72                                                   copolymer     74        .26                                                   ______________________________________                                    

These assays indicate that the copolymer of Example 5 is effective inprevention of CaSO₄ and CaCO₃ scale.

The following examples will serve to illustrate the tartar barriercompositions of this invention. Copolymers of Examples 1, 2 and 5 aresuitable tartar barrier agents. Humectants are materials such asglycerol. Foaming agents are suitable surfactants. Sweetening agents maybe normal or artificial sweeteners. Common abrasives are materials likefumed silica. Gelling agents are polymers which are used to preparethickened solutions.

    ______________________________________                                                             % w/w                                                    ______________________________________                                        EXAMPLE A-Mouthwash                                                           Tartar barrier agent   0.5-2                                                  humectant              6.0                                                    foaming agent          1.0                                                    sweetener              0.3                                                    deionized water        q.s. to 100                                            flavors                1.0                                                    EXAMPLE B-Abrasive Dentifrice Gel                                             Tartar barrier agent    2-10                                                  detergent              1.5                                                    humectant              10.0                                                   sweetener              0.2                                                    deionized water        q.s. to 100                                            flavors                1.0                                                    abrasive               55.0                                                   gelling agent          2.0                                                    EXAMPLE C-Chewing gum                                                         Tartar barrier agent   1.0-11                                                 Gum base               21.3                                                   sugar                  48.5-58.5                                              corn syrup             18.2                                                   flavors                1                                                      ______________________________________                                    

It will be apparent to those skilled in the art that the examples andembodiments described herein are by way of illustration and not oflimitation, and that other examples may be utilized without departingfrom the spirit and scope of the present invention, as set forth in theappended claims.

We claim:
 1. A process for the preparation of copolymers of polyasparticacid comprising reacting maleic acid, a polycarboxylic acid and ammonia,at temperatures of 120°-350° C., and converting the resultant polymerinto a salt by adding a hydroxide.
 2. The process of claim 1 wherein thepolycarboxylic acid is selected from the group consisting of adipicacid, citric acid, fumaric acid, malic acid, malonic acid, succinicacid, glutaric acid, oxalic acid, pimelic acid, itaconic acid,nonanedioic acid, dodecanedioic acid, octanedioic acid, isophthalic,terphthalic and phthalic acid.
 3. The process of claim 1 wherein thetemperature is 200°-300° C.
 4. A method of preventing deposition ofscale from mineral containing water comprising the addition of aneffective amount of a copolymer of polyaspartic acid with apolycarboxylic acid to said water.
 5. A method of preventing depositionof scale from mineral containing water comprising the addition of aneffective amount of a copolymer of polyaspartic acid, a polycarboxylicacid, and a polyamine.